1. Field of the Invention
The invention relates to a device for sensing an obstacle in the opening range of an automotive closure element movable between an open position and closed position, more particularly an electrically powered door window or sunroof. The device is provided for sensing an obstacle in the opening range of the closure element with a sensor comprising at least one electrical conductor generating an electrical field in the opening range of the closure element.
2. Background Art
Devices of this kind are trapping protectors serving to prevent part of the human body being trapped, for instance, between a powered door window and at least some part of the edge surrounding the window. For this purpose known devices feature a sensor which senses the presence of an obstacle in the opening range of the window representing the closure element and furnishes a signal controlling the motor powering the window. As regards the function of the sensor a distinction is made between trapping protectors requiring physical contact with the obstacle and trapping protectors working by proximity (non-contact) sensing.
One such trapping protector belonging to the first group is described, for example, in DE 199 13 105 A1. This known device comprises a weatherseal sealing a closure element and is engineered with two electrically conductive portions spaced away from each other. When physical contact occurs with an obstacle in the opening range of the closure element the electrically conductive portions are pressed together, resulting in a switching contact which triggers an electrical control signal.
A proximity-type trapping protector is disclosed in EP 0 648 628 B1. This known device comprises an electrical conductor which generates an electrical field in the opening range of a powered window pane. The presence of an obstacle results in a change in the dielectric constant in the opening range which becomes evident by a change in frequency, phase or amplitude of an oscillating circuit generating the electrical field through the conductor. This change is analyzed to generate a signal for controlling the motor powering the window. The conductor emitting the electrical field is arranged on a weatherseal sealing the window pane whilst serving to strengthen the weatherseal.
Known from EP 1 154 110 A2 is a proximity or non-contact type trapping protector. The way in which this trapping protector works is based on a change in capacitance of an electrical field generated between two electrical conductors prompted by an electrically conducting obstacle. One of the two conductors, the sensor electrode, is integrated in a weatherseal sealing the closure element and receives a predefined electric charge. It is in this way that between the sensor electrode and the other conductor, the basic electrode which is for example an automotive frame to which the weatherseal is secured, a reference capacitance can be defined, a change in which caused by an obstacle triggers a signal for controlling the motor powering the closure element. The basic electrode may also be formed by a conductor likewise integrated in the weatherseal. The effect of the electrical field in this case depends on the arrangement of the sensor electrode with respect to the basic electrode.
Experience has shown that the disadvantage of this known device is that movement of the closure element is evident as an interference to the reference capacitance. Although this nuisance can be compensated by an electronic circuit this is relatively complicated. Apart from this, orienting the electrical field by a suitable arrangement of sensor electrode and basic electrode has proven to be unsatisfactory, since although this enables the interference by the closure element to be reduced, it still cannot be eliminated completely.